ios 任务、线程、定时器

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一：operations（任务）

 

cocoa提供了三种不同的operations

 

1：Block operations（NSBlockOperation）
These facilitate the execution of one or more block objects.

 

 

#import 
@interface OperationsAppDelegate : NSObject  {
	UIWindow *window;
	NSBlockOperation *simpleOperation;
}

@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) NSBlockOperation *simpleOperation;

@end

 

#import "OperationsAppDelegate.h"

@implementation OperationsAppDelegate
@synthesize window;
@synthesize simpleOperation;

- (BOOL) application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
	/* Here is our block */
	NSBlockOperation *newBlockOperation = [NSBlockOperation blockOperationWithBlock:^{
							NSLog(@"Main Thread = %@", [NSThread mainThread]);
							NSLog(@"Current Thread = %@", [NSThread currentThread]);
							NSUInteger counter = 0;
							for (counter = 0;counter < 1000;counter++){
								NSLog(@"Count = %lu", (unsigned long)counter);
							}
								}];

	/* Make sure we keep the reference somewhere */
	self.simpleOperation = newBlockOperation;
	
	/* Start the operation */
	[self.simpleOperation start];

	/* Print something out just to test if we have to wait
	for the block to execute its code or not */
	
	NSLog(@"Main thread is here");
	[window makeKeyAndVisible];
	return YES;
}


- (void)dealloc {
	[simpleOperation release];
	[window release];
	[super dealloc];
}

@end

 

 

2：Invocation operations（NSInvocationOperation）
These allow you to invoke a method in another, currently existing object.

 

NSNumber *simpleObject = [NSNumber numberWithInteger:123];

NSInvocationOperation *newOperation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(simpleOperationEntry:) object:simpleObject];

[newOperation  start];

 

 

调用start方法执行改任务

 

#import 
@interface OperationsAppDelegate : NSObject  {
	UIWindow *window;
	NSInvocationOperation *simpleOperation;
}

@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) NSInvocationOperation *simpleOperation;

@end

 

- (void) simpleOperationEntry:(id)paramObject{

	NSLog(@"Parameter Object = %@", paramObject);
	NSLog(@"Main Thread = %@", [NSThread mainThread]);
	NSLog(@"Current Thread = %@", [NSThread currentThread]);
}

- (BOOL) application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

	NSNumber *simpleObject = [NSNumber numberWithInteger:123];
	NSInvocationOperation *newOperation =[[NSInvocationOperation alloc] initWithTarget:self selector:@selector(simpleOperationEntry:) object:simpleObject];
	self.simpleOperation = newOperation;
	[newOperation release];

	[self.simpleOperation start];
	[window makeKeyAndVisible];
	return YES;
}

- (void)dealloc {

	[simpleOperation release];
	[window release];
	[super dealloc];
}

 

 

 

 

 

 

3：Plain operations（简单的任务）NSOperation的子类

These are plain operation classes that need to be subclassed. The code to be executed
will be written inside the main method of the operation object.

 

 

@interface MyTask : NSOperation { 
    int operationId; 
}

@property int operationId;

@end

 

这里的operationId属性不是必须的

 

@implementation MyTask

@synthesize operationId;

- (void)main{ 
    NSLog(@"task %i run … ",operationId); 
    [NSThread sleepForTimeInterval:10]; 
    NSLog(@"task %i is finished. ",operationId); 
}

@end

 

 

必须
- (void)main;方法，[MyTask start]是执行main方法

 

 

二：任务队列（NSOperationQueue）

 

NSOperationQueue *newOperationQueue = [[NSOperationQueue alloc] init];
[ newOperationQueue  addOperation:Operation];

 

 

以上三种Operation都可以添加到NSOperationQueue中，添加后立即被执行。

 

NSOperationQueue 可以设置最大并行执行任务数。默认值为-1无限制。

 

 

三：多个任务之间存在依赖关系

 

设置方式：

[self.firstOperation addDependency:self.secondOperation];

 

dependency：附属的意思

 

把secondOperation做为firstOperation的附属。因此先执行secondOperation，再执行firstOperation 。

 

 

四：延时执行某个方法

 

1：performSelector:withObject:afterDelay:

 

 

- (void) connectionHasFailedWithError:(NSError *)paramError onRemoteURL:(NSURL *)paramRemoteURL{
	/* We failed to download the file. Attempt to download it again after 3 seconds */
	[self performSelector:@selector(attemptToDownloadRemoteURL:) withObject:paramRemoteURL afterDelay:3.0f];
}

- (void) attemptToDownloadRemoteURL:(NSURL *)paramRemoteURL{
	/* Attempt to download the remote file again here by initializing
	a new connection ... */
}

 

该方法只能接受一个参数。如果需要传递多个参数怎么办呢???

     让selector调用的方法接受的参数类型修改为Dictionary类型。

 

 

（1）如果调用的selector不接受参数则，withObject：nil

（2） 通过performSelector:withObjcet:afterDelay调用的方法不能有返回值

 

 

2：取消延时执行的方法

 

（1）cancelPreviousPerformRequestsWithTarget: 

（2） cancelPreviousPerformRequestsWithTarget:selector:object:

 

 

五：NSTimer

 

1：scheduledTimerWithTimeInterval:target:selector:userInfo:repeats:

 

2：invalidate

调用invalidate方法，不仅是释放NSTimer，还释放userinfo对象。
如果repeats设置为NO，NSTimer在调用完成之后就知道失效，随即释放userinfo对象

 

3：scheduledTimerWithTimeInterval:invocation:repeats:

 

- (void) startPainting{
 	SEL selectorToCall = @selector(paint:);
 	NSMethodSignature *methodSignature = [[self class] instanceMethodSignatureForSelector:selectorToCall];
 	NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSignature];
	[invocation setTarget:self];
	[invocation setSelector:selectorToCall];

/* Start a scheduled timer now */
NSTimer *newTimer =[NSTimer scheduledTimerWithTimeInterval:1.0
						invocation:invocation
						   repeats:YES];

	self.paintingTimer = newTimer;
}

 

 4：timerWithTimeInterval:target:selector:userInfo:repeats:

   （用该方式，需要把timer添加到runloop中）

 

- (void) startPainting{
	NSTimer *newTimer = [NSTimer timerWithTimeInterval:1.0
						    target:self
						  selector:@selector(paint:)
						  userInfo:nil
						   repeats:YES];

	self.paintingTimer = newTimer;

	[[NSRunLoop currentRunLoop] addTimer:self.paintingTimer forMode:NSDefaultRunLoopMode];
}

 

5：timerWithTimeInterval:invocation:repeats:

  （用该方式，需要把timer添加到runloop中）

- (void) startPainting{ 
	SEL selectorToCall = @selector(paint:);
 	NSMethodSignature *methodSignature =[[self class] instanceMethodSignatureForSelector:selectorToCall];
 	NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSignature];

	[invocation setTarget:self];
	[invocation setSelector:selectorToCall];
	NSTimer *newTimer = [NSTimer timerWithTimeInterval:1.0
						invocation:invocation
						   repeats:YES];
	self.paintingTimer = newTimer;
 	[[NSRunLoop currentRunLoop] addTimer:self.paintingTimer
				     forMode:NSDefaultRunLoopMode];
}

 

 

6：NSTimer 响应函数定义格式

 

并需有一个NSTimer *类型的参数

 

- (void) paint:(NSTimer *)paramTimer{
	/* Do something here */
	NSLog(@"Painting");
}

 

 

 

六：NSThread

 

1：initWithTarget:selector:object:

 

2：detachNewThreadSelector:toTarget: withObject:

 

以上两种方式，selector调用的函数，必须声明自己的NSAutoreleasePool

 

 

3：performSelectorInBackground: withObject:

     一个简单的方法来创建线程，而无需直接处理线程。

[self performSelectorInBackground:@selector(thirdCounter) withObject:nil];

 

4:start

调用start方法启动线程

 

5:cancel

调用cancel方法，并把变量赋值为nil

 

6:cancel vs exit

 

对于线程调用cancel方法停止，不要调用exit，因为exit方法没有给线程清理自己并释放资源的时间

 

7:线程的内存泄露

 

 - (void) newThreadEntryPoint{
	/* A thread without an autorelease pool to test the following code */
	//NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
	
	/* This WILL cause a memory leak */
	[self performSelector:@selector(allocateSomething)];

	/* This will NOT cause a memory leak */
	[self performSelectorOnMainThread:@selector(allocateSomething)
				withObject:nil
			     waitUntilDone:YES];
	//[pool release];
}

- (void) allocateSomething{
	NSBundle *mainBundle = [NSBundle mainBundle];
	NSString *imagePath = [mainBundle pathForResource:@"MyImage" ofType:@"png"];
	NSData *imageData = [NSData dataWithContentsOfFile:imagePath];
	UIImage *myImage = [[[UIImage alloc] initWithData:imageData] autorelease];
	/* Do something with the image here */
}

- (void)viewDidLoad {

	[NSThread detachNewThreadSelector:@selector(newThreadEntryPoint)
				 toTarget:self
			       withObject:nil];
}

 

 

UIImage *myImage = [[[UIImage alloc] initWithData:imageData] autorelease];-------------自动释放池的范围

 

/* This WILL cause a memory leak */
[self performSelector:@selector(allocateSomething)];

调用改方法myImage 对象被添加进该新建线程的自动释放池，但因为在这里没有声明NSAutoreleasePool 造成内存泄露

 

 /* This will NOT cause a memory leak */
[self performSelectorOnMainThread:@selector(allocateSomething)
withObject:nil
     waitUntilDone:YES];

 

调用改方法myImage 对象被放进主线程的自动释放池，在主线程销毁是被自动释放